1. 一對多的關聯關系

1.1. 角色和用戶是一對多的關聯關系

角色類(對應表名: t_role): 一方

用戶類(對應表名: t_user): 多方

1.2. 角色表

1.3. 用戶表?

2. 一對多的關聯關系例子

2.1. 創建一個名為spring-data-jpa-one2many的Java項目, 同時添加相關jar包, 并添加JUnit能力。

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2.2. 新建Role.java?

package com.bjbs.pojo;import java.io.Serializable; import java.util.HashSet; import java.util.Set; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.OneToMany; import javax.persistence.Table;@Entity // 指定該類是實體類 @Table(name = "t_role") // 指定數據庫表名(表名和實體類對應) public class Role implements Serializable {private static final long serialVersionUID = 1L;@Id // 指定為主鍵@GeneratedValue(strategy = GenerationType.IDENTITY) // 指定主鍵生成策略@Column(name = "id") // 指定表中列名(列名和屬性名對應)private Integer id;@Column(name = "name")private String name; // 角色名@OneToMany(mappedBy="role")private Set<User> users = new HashSet<User>();public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Set<User> getUsers() {return users;}public void setUsers(Set<User> users) {this.users = users;}@Overridepublic String toString() {return "Role [id=" + id + ", name=" + name + "]";}}

2.3. 新建User.java

package com.bjbs.pojo;import java.io.Serializable; import javax.persistence.CascadeType; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.ManyToOne; import javax.persistence.Table;@Entity // 指定該類是實體類 @Table(name = "t_user") // 指定數據庫表名(表名和實體類對應) public class User implements Serializable {private static final long serialVersionUID = 1L;@Id // 指定為主鍵@GeneratedValue(strategy = GenerationType.IDENTITY) // 指定主鍵生成策略@Column(name = "id") // 指定表中列名(列名和屬性名對應)private Integer id;@Column(name = "name")private String name; // 用戶名@ManyToOne(cascade=CascadeType.PERSIST)// @JoinColumn: 就是維護一個外鍵@JoinColumn(name="r_id")private Role role;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Role getRole() {return role;}public void setRole(Role role) {this.role = role;}@Overridepublic String toString() {return "User [id=" + id + ", name=" + name + "]";}}

2.4. 新建UserRepository.java

package com.bjbs.dao;import org.springframework.data.jpa.repository.JpaRepository; import com.bjbs.pojo.User;/*** 參數一T: 當前需要映射的實體; 參數二 T: 當前映射的實體中的id的類型*/ public interface UserRepository extends JpaRepository<User, Integer> {}

2.5. 新建TestUserRepository.java

package com.bjbs.test;import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.test.context.ContextConfiguration; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner; import com.bjbs.dao.UserRepository; import com.bjbs.pojo.Role; import com.bjbs.pojo.User;@RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration("classpath:applicationContext.xml") public class TestUserRepository {@Autowiredprivate UserRepository userRepository;@Testpublic void findOne() {User user = userRepository.findOne(2);System.out.println(user);Role role = user.getRole();System.out.println(role);}@Testpublic void save() {// 新建用戶User user = new User();user.setName("翠花");// 新建角色Role role = new Role();role.setName("測試人員");// 建立關系role.getUsers().add(user);user.setRole(role);// 保存用戶userRepository.save(user);} }

2.6. 在src下新建application.properties

spring.datasource.driverClassName=com.mysql.cj.jdbc.Driver spring.datasource.url=jdbc:mysql://192.168.25.138:3306/StudyMybatis?useSSL=true&useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai spring.datasource.username=root spring.datasource.password=lyw123456

2.7. 在src下新建applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns="http://www.springframework.org/schema/beans"xmlns:context="http://www.springframework.org/schema/context"xmlns:tx="http://www.springframework.org/schema/tx"xmlns:jpa="http://www.springframework.org/schema/data/jpa"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsdhttp://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa.xsdhttp://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd"><!-- 配置讀取properties文件的工具類 --><context:property-placeholder location="classpath:application.properties" /><!-- 配置c3p0數據庫連接池 --><bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource"><property name="jdbcUrl" value="${spring.datasource.url}" /><property name="driverClass" value="${spring.datasource.driverClassName}" /><property name="user" value="${spring.datasource.username}" /><property name="password" value="${spring.datasource.password}" /></bean><!-- Spring整合JPA 配置EntityManagerFactory --><bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"><property name="dataSource" ref="dataSource" /><property name="jpaVendorAdapter"><bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter"><!-- hibernate相關的屬性的注入 --><!-- 配置數據庫類型 --><property name="database" value="MYSQL" /><!-- 正向工程 自動創建表 --><!-- <property name="generateDdl" value="true" /> --><!-- 顯示執行的SQL --><property name="showSql" value="true" /></bean></property><!-- 掃描實體的包 --><property name="packagesToScan"><list><value>com.bjbs.pojo</value></list></property></bean><!-- 配置Hibernate的事務管理器 --><bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager"><property name="entityManagerFactory" ref="entityManagerFactory" /></bean><!-- 配置開啟注解事務處理 --><tx:annotation-driven transaction-manager="transactionManager" /><!-- 配置springIOC的注解掃描 --><context:component-scan base-package="com.bjbs.service" /><!-- Spring Data JPA 的配置 --><!-- base-package: 掃描dao接口所在的包 --><jpa:repositories base-package="com.bjbs.dao" /> </beans>

2.8. 查詢一個用戶

2.9. 保存一個用戶?

總結

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